1. Field of the Invention
This invention relates generally to engine combustion components for internal combustion engines, and methods of manufacturing the same.
2. Related Art
Modern heavy duty diesel engines are being pushed towards increased efficiency under emissions and fuel economy legislation. To achieve greater efficiency, the engines must run hotter and at higher peak pressures. Thermal losses through the combustion chamber can be problematic under these increased demands. For example, typically about 4% to 6% of available fuel energy is lost as heat through the piston into the cooling system. One way to improve engine efficiency is to extract energy from hot combustion gases by turbo-compounding. For example, about 4% to 5% of fuel energy can be extracted from the hot exhaust gases by turbo-compounding.
another approach to improving engine efficiency is to insulate the crown of the piston in order to reduce the heat otherwise lost to the cooling system. Insulating layers of ceramic are one approach to insulating the piston. It is known to apply a metal layer to the body portion of the piston followed by application of a ceramic layer. However, ceramic is inherently porous and the combustion gases can pass through the ceramic layer and oxidize the metal layer causing a failure at the ceramic/metal layer interface and eventual spalling and failure of the ceramic layer. There is also a mismatch in the thermal expansion coefficients of the ceramic and metal layer, further adding to the potential delamination and spalling of the ceramic layer over time.
another example is a thermally sprayed coating formed of yttria stabilized zirconia. This material, when used alone, can suffer destabilization through thermal effects and chemical attack in diesel combustion engines. It has also been found that thick ceramic coatings, such as those greater than 500 microns, for example 1 mm, are prone to cracking and failure.
Although more than 40 years of thermal coating development for pistons is documented in literature, there is no known product that is both successful and cost effective to date. It has also been found that typical aerospace coatings used for jet turbines are not suitable for engine pistons because of raw material and deposition costs associated with the highly cyclical nature of the thermal stresses imposed.
Another approach to piston protection specific to aluminum pistons is to convert the surface of the aluminum crown to aluminum oxide via plasma oxidation and then the pores of the conversion layer are sealed with polysilazane. The conversion zone is very thin (50-70 microns) and is understood to be a high insulation and dissipation material that quickly heats and cools so it cycles with the heat of combustion. This relatively thin conversion approach for aluminum pistons has no application for use with steel or other iron-based pistons.